1. Field of the Invention
The present invention generally relates to a communication system, and more particularly to robust reception of a packet-based asynchronous communication over a noisy channel.
2. Description of Related Art
Asynchronous transmission mode (or asynchronous transfer mode, ATM) is a packet-oriented transfer technology that transfers finite-length packets in the “physical layer.” The asynchronous transmission mode is widely adapted to, for example, Teletext, closed captioning (CC), and Video Programming System (VPS) contexts in broadcast television systems (e.g., NTSC, PAL or SECAM), as well as 10BASE Ethernet and wireless local area network (e.g., IEEE 802.11) protocols.
In a transmitter of the asynchronous transmission mode, during an idle or silent period no signal is transmitted (from the physical layer) through the transmission media until the data link layer makes a request. On the other hand, before a receiver of the asynchronous transmission mode may effectively and correctly recover the transmitted data, some pre-measures have to be performed such as signal level estimation and compensation, channel estimation/equalization, carrier synchronization, symbol synchronization, and frame synchronization.
In order to facilitate those pre-measures, a preamble (or clock run-in) and a frame code (or start-of-frame delimiter, SFD) are incorporated (by the “data link layer”) preceding the “data body” that contains the transmitted information. FIG. 1 shows a waveform of a transmitted packet. The preamble is used to assist the receiver in performing the signal level/channel estimation, channel estimation/equalization and symbol synchronization; the frame code is used to help the receiver determine the beginning of the data body.
Specifically, a predefined SFD pattern is compared to the received word to determine the end of the SFD, or in other words, the beginning of the data body. For example, “10101011” is used as the predefined SFD pattern in the 10BASE Ethernet protocol. Nevertheless, for a low signal-to-noise (SNR) noisy channel, particularly in a wireless or long-haul communication system, it may be probable that either the predefined SFD pattern is never matched to the received SFD (i.e., mismatching), resulting in data loss, or that a portion other than the received SFD is mistaken for the predefined SFD (i.e., false matching), resulting in an invalid packet reception. In order to resolve these situations, a loose partial matching scheme is usually used instead, whereby one or more bits of the predefined SFD pattern are allowed to be overlooked. However, the partial matching scheme increases the probability of false matching.
FIG. 2A to FIG. 2E show some SFD matching examples. In FIG. 2A, the predefined SFD pattern (“11100100” in the example) is fully matched to the received SFD. In FIG. 2B, a received datum has been corrupted in a noisy channel. The received bit (Rx_Bit) with a dashed circle is an error bit caused by noise. The predefined SFD pattern will be mismatched if the full matching scheme is used. FIG. 2C shows multiple error bits corresponding to more received data having been corrupted in the noisy channel. Accordingly, the predefined SFD pattern will be falsely matched if the full matching scheme is used. In FIG. 2D, a partial matching (e.g., 7-bit partial matching) scheme is used, and, accordingly, the predefined SFD pattern is falsely matched. In FIG. 2E, a looser partial matching (e.g., 6-bit partial matching) scheme is used, and, accordingly, the predefined SFD pattern is also falsely matched.
For the reason that conventional partial matching methods tend not to effectively and correctly determine the beginning of the data body, a need has arisen to propose a novel partial matching scheme that can improve the conventional partial matching.